The present invention relates to an image processing apparatus and an image processing method for conducting a width adjustment processing of a line image represented by predetermined black pixels in a binary image constituted by white pixels and black pixels.
Conventionally, in the market, there has been an image outputting apparatus that forms an image on a transfer material by employing an electro-photographic method including the steps of: forming a latent image on an image bearing member, such as a photoreceptor drum, etc., by scanning a laser beam onto the surface of the image bearing member so as to expose the image bearing member to the image; developing the latent image with toner so as to form a toner image; directly transferring the toner image onto the transfer material, or primary transferring it onto an intermediate transfer member and secondary transferring it onto the transfer material from the intermediate transfer member; and fixing the toner image onto the transfer material by employing a fixing device.
If the toner adhesion appearance in respect to the transfer material were bad in such the image outputting apparatus as mentioned in the above, some portions of the image would be blurred, resulting in deterioration of the image quality as a whole. Further, since a little number of pixels constitute each of the lines included in characters, such the characters are specifically liable to be blurred, and sometimes, it becomes difficult to read such the characters.
Accordingly, in order to improve the toner adhesion appearance, it had been made effort to improve the adhesive property of the toner, by enlarging a dimension of each pixel as large as possible at a predetermined resolution, so as to enlarge the adhesive area of toner.
The larger the dimension of each pixel is made, the better the adhesive property of the toner becomes. However, for instance as its side effect, sometimes, it has occurred that a line was formed bolder than expected, or a white space area was formed smaller than expected. As a result, sometimes, there has occurred such problems that spaces between fine lines were filled with black toner as if it were a solid image, and the characters formed by such the filled line were illegible.
Accordingly, in order to cope with the abovementioned problems, the number of pixels constituting the width of the line has been changed, while enlarging the dimension of the pixel as larger as possible so as to maintain the adhesive property of the toner, so that the width of the line constituted by the black pixels did not become bold and the white space did not become small. For instance, there has been proposed a countermeasure that makes it possible to narrow the width of the line by changing black pixels located adjacent to white pixels and constituting an edge in a line and a character (edge pixels) to white pixels
For instance, as an apparatus that conducts the line thinning operation, Patent Document 1 (Tokkaihei 2-268374, Japanese Non-Examined Patent Publication) sets forth an apparatus that conducts the processing for thinning the line width to that equivalent to one pixel width. The processing includes the steps of: comparing the 3×3 pixel value pattern with the mask provided in advance; determining whether or not there is a possibility that the target pixel is converted to a new value by pixel values of the pixels located adjacent to the black pixels; finally determining whether or not the pixel value of the pixel, which is determined that there is the abovementioned possibility, should be further converted by the pixel values of the peripheral pixels by employing another mask; etc.
Since the line thinning operation, conducted by the apparatus set forth in Patent Document 1 (Tokkaihei 2-268374, Japanese Non-Examined Patent Publication), includes the multi-stage determining steps and processing, and accordingly, takes much time, it is desirable that the processing is further simplified and the processing time is further shortened. However, when the line thinning operation was achieved by, for instance, simply changing the edge pixels to the white pixels, sometimes the image quality has been deteriorated, due to the fact that the continuity and the shape of the concerned line could not be maintained, or an isolated pixel would be generated. In other words, it has been uneasy to simplify the processing for the line thinning operation while maintaining the original image quality.
Further, the term of the line thinning operation indicates not only the processing for thinning the line width to that equivalent to one pixel width, but also a method for making it possible to thin the line width to that equal to or greater than two pixel width, and desirably, a method for making it possible to widen the width of a white space (namely, a line constituted by the white pixels).
Although the degree of line thinning, such as changing a line constituted by two pixels to that of a single pixel, leaving a line constituted by two pixels as it is, etc., would vary depending on the user's taste or other factors, it has been difficult to easily cope with such the variations of the tastes or demands.